Rubber printing plate



v s vif J. c. BAKER LSSQJQ RUBBER PRINTING PLATE Fied March 24, 1928 2swam-smet 2 x n i? 7 gli# 5 provide a method of makin Patented Dec. l,1931 PATENT OFFICE JOHN C. BAKER, F NUTLEY, NEW JERSEY, .ASSIGNOR TOWALLACE & TIERNAN Y ERGDUCTS, INC., 0F BELLEVILLE, NEW JERSEY, ACORPORATION 0F NEW JERSEY RUBBER PRINTING PLATE Application led March24, 1928. Serial No. 264,329.

rl"his invention relates enerally to printing and has particular reerence to the making of rubber printing lates.

One of the objects o this invention is to metal-backed rubber printingplates whic are accurate reproduction in all essential particulars of anengraved or etched die or master late.

Another object of the invention 1s to provide improvements in knownapparatus for producing rubber printing plates which, in addition toother characteristics, will be of the same thickness as the master plateor die used inmaking the plates.

@ther objects and advanta es will be apparent from the disclosuresereinafter set forth, in connection with the drawings which accompanyand form a part of thls specication. Y

w In said drawings:

Fig. 1 shows a suitable press and associated elements for performing oneof the early steps involved in the making of metal-backed rubberprinting plates.

Fig. 2 is a cross section illustrating a resuit of the operation of theapparatus of `Fi l.

gigs. 3 and 4 illustrate the apparatus and method of producing a leadlined, rigid mold e upon the master plate.

Fig. 5 shows how the master plate is referably removed from the leadlined mol and Fig. 6 is a cross section through the lead lined mold fromwhich the master plate has Fig. 7 shows the essential features of thenew apparatus which comprises a vulcanizing press which is more or lessconventionally represented. Y v

t1 Fig. 8 shows how the mold may, if desired,

be stripped from the finished rubber print-` i these limiting factors isthat it has been im-V possible to get accurate alignnient orregistration when printing from such plates, due to unavoidablevariations between them and what are, for convenience, usually referredto herein as the dies or master plates. Such dies or plates areproduced' in various ways, such as by casting, etching or engraving andare true to the dimensions of the picture or: design which is to beproduced.

The variations between the rubber plates of the rior art and the masterplates arise partly rom the fact that the molds in which the rubber isformed to 've the printing design, do not expand at t e same ratev asthe rubber in vulcanizing, and when the finished plates are removed fromthe vulcanizing mold and cooled, it is found that the rubber has shrunkso that the plates are smaller than the original, and that the variouselements of the design or picture are out of their correct relativepositions.

In prior manufactures the rubber plates have, after vulcanization, beenmounted on metal or wooden lates so that the can be carried in aprintlng press. It has een apreciated that this attaching operationmight e made a part of the vulcanizing operation, and thati the rubberplates could be vulcanized on metal backing plates shrinking and otherharmful variations from the master plates might largely be revented.However, in prior manufactures 1t has been found dificult to effect suchvulcanization on the backing because of the nature of the molds employedand the methods of usin them in manufacturing. While attempts ave beenmade along the line indicated, they have, so far as known, been"unsatisfacto because of the high percentage of damag or defectiveplates.

It has now been discovered how these difl ficulties can be overcome andan accurate un damaged plate produced which is vulcanized to a-metalbacking of sufficient stiffness to prevent any subsequent shrinking ofthe rubber or displacement of the rubber.

Stated in general terms the new way of manufacturing such platescomprises the use of lead lined, special molds for the rubber formingand vulcanizing operations. Such a mold is produced by first copying ina sheet of lead the outline and surface configuration of a die or masterlate. In making the copy the sheet of leadp is forced into and over themaster plate b pressure.

In order that t e lead may faithfully receive all of the details of vthemaster plate, the pressure is applied by any suitable press through apad o yielding material which is fibrous enough to revent breaking thepad down too readily, ut which kwill yield suficiently to cause asatisfactory distribution of the pressure. A pad of dry paper pulp orone composed of sheets of newspaper gives very satisfactory results.Applying the press ure throu h such a pad forces the lead into all ofthe details of the die or master plate, thereby effecting a veryaccurate embossing in the lead of all features of the picture ordesign.r The pressure is then released and the pad removed, leaving thelead pressed into and Varound the master plate.

A backing is then a plied which is rigid and which will hold t e design-in the lead after .the lead is removed from the master plate. For thisApurpose a material is used which can be poured over the lead sheet andmaster plate and whichwill set to a rigid form. A satisfactory materialis a mixture of lycerine and litharge or a dent-al cement. Beorestarting the pouring operatlon the master plate, and the adhering leadsheet, is laid on a`truly flat surface, and after pouring, and/'beforethe material hasvhad ytime to set, asimilar truly fiat plate is used toforce the material down until this second plate vis arrested by stopsrovided for that purpose. These stopsare o such height that suic1entbacking material remains behind thevlead t0 give ample rigidity at allpoints.

After the backing has set, the master plate, with the attached rigidbacking, is removed from the supporting and pressure plates..

The master plate is then removed, leaving a lead lined mold which isready for use in molding and vulcanizing rubber plates. In the preferredpractice this lead lined mold is not quite as deep as the thickness ofthe master plate, the reasons for this difference and the way in whichit is obtained being hereinafter explained in detail. l

The lead lined mold is then placed between relatively movable plates ofa. vulcanizing press havin their faces truly `fiat and parallel.Eitherefore or after placing the mold in the press, it is supplied witha suitable plastic rubber compound containing the usual or any desiredvulcanizing and similar agents, the quantity of the compound being inexcess of that required for the finished plate. v A backing platepreviously treated to cause adhesion of the rubber is then applied tothe compound and the vulcanizing press operatated to force that platetoward the mold. This compacts the compound in all of the details of thelead lined mold, and extrudes the excess rubber between the top of themold and the backing plate. Stops between the relatively movableportions of the vulcanizing press arrest that movement at the pointwhere the thickness through the rubber and backing plate issubstantially the same as the thickness of the die or master plate usedin making the mold. As a result, after the vulcanization is completedthe finished rubber plate will be a metal backed rubber reproduction ofthe master plate in dimensions and all yother essential characteristics.The metal backing plate em loyed is preferably composed of an allo olead and antimon Such a material as the necessary rigi ity to hold therubber in position, but is nevertheless capable of being formed tooffset irregularities or regulate the impression of the printing face.Such a metal or. alloy presents diiculties in the way of gettinor a goodadhesion of the rubber and the bac ing plate, but it has been discoveredthat if the face of the late which engages the rubberis washed with adilute solution containing copper sulphate and copper nitrate a perfectadhesion will result from the molding and vulcanizing operation.

Describing the apparatus and the manufacture more in detall and withreference to the drawings, a book press 10, such as is shown in Fig. 1,may be employed when the sizes of the printing plates required do notnecessitate a greater press capacity. In making larger plates ahydraulic or other more i powerful press may be em loyed.

The top surface of the be 11, and the lower face 12 of the laten 13 ofthe press should both be Hat and) substantially parallel.

At the start of the iperation the master I plate 14 which is tobefreproduced is placed face up on the bedof the press. Strips of paperor metal 15 are then placed on-tlie bed and around the master plate anda sheet 16 of lead laid over the face of the master l plate.Superimposed on the sheet of lead is a yielding ad 17 which ispreferably of a somewhat fi rous nature, a suitable material being drypaper pulp or a number of plies of newsprint paperf l rl.`he press 10 isthen operated to apply pressure through the pad 17 to force the lead 16into and over the master plate and into contact with the strips 15around the master plate 14. Sto s 18 serve to prevent movement Yl of theplaten ar enough to have a destructive eii'ect upon the lead. As aresult of the press operation the llead sheet is embossed and shaped tothe master plate as illustrated in Fig. 2. Examination of Fig. 2 willshow 4-1 that the side portions or extensions 16 of the lead are, owingto the eii'ect of the strips 15, parallel to and slightly above the backofthe jmaster plate.

The'master plate, with the adhering lead, 1

is then laid on a truly flat surface 18, Fig. 3, of a block or plate 19,with the lead covered face up, after which a bac-king for the lead isapplied. This backing is .preferably of a material which can be appliedin iiuid condition and which will set readily, but which will also belsufticientl rigid and strong to stand pressing and vu canizingoperations. This material may be varied, but a mixture of glycerine andlitharge or dental cement has been found very satisfactory. Beforestarting the pouring opera/tion it may be necessary to support theportions 16 of the lead sheet by strips similar to the strips 15 used inthe matrix forming press 10, as it is desirable that the portions 16 bemaintained in substantially the positions given them in the press.

As soon as the pouring is completed and before the backing material hasbegun to set, a plate 2l (Fig.,4) accurately machined to give a trulyiat'surface is laid on the material and forced down by gravity, assistedby a hand pressureor by a weight 22, if desired,

' l until arrestedby stops 23. These stops might be permanently attachedto the block 19 when a number of molds of the same depth are to beprepared or they may be interchangeable to suit varying conditions. Theymustalways be of suilicient height to'provide for a backing ofsufficient thickness to properly support the lead.

After the backing has set, the mast-er plate 14 and the backed leadsheet are removed from the press and the master plate/then removed. Thisis accomplished or assisted by directing a jet of air 24 around the edgeof the master plate as illustrated in Fig. 5. Thisleaves a lead linedmold 25, illustrated in Fig. (i,v

which is slightly less in depth than the thickness or height of themaster plate, and which contains a true copy of the master plate.

The mold is then supplied with rubber compound in plastic condition asshown at 27 s in Fig. 7, the quantity of compound, being y preferablyconsiderably in excess of the quantity of rubber which will be found inthe finished article. -A backing plate 28 is then laid on the compoundand the assembly introduced between the relatively movable ele: ments 31and 32 of a vulcanizing press of a known type but which have theiropposing faces truly fiat and parallel when closed. The press is nextoperated to mold the'rubber and vulcanize it.

The relative movement of the elements 31 and 32 compresses the rubberplastic in the moldv and extrudes the excess between the edges 34 (Figs.6 and 7) of the mold and the backing plate 28. The strips 15 (Fig. 1)were used so as to provide a clearance between the plate and mold which.while preventing to'o free an extrusion, will permit the excess rubberto escape. The extruded portions 35 of the rubber are later trimmed olf.

In 'order to limit the relative movements of the press members 31 and 32to produce a mounted rubber plate of the desired thick ness, stops 36are employed. These stops should preferably be of the same height as thestops 23 (Fig. 4) in the mold forming press, if the finished platedesired is to have the same thickness as the master p'late. If afinished plate of a thickness different from that of the master plate isdesired the stops 36 should be adjusted accordingly.

The molds are not re-used and may be stripped from the finished platesin the manner illustrated in Fig. 8 by means of the sheet of lead 16. I

The composition of the metal backin g plate andthe manner in which it isprepared to secure firm adhesion of the rubber to the metal were,explained above, and repetition is unnecessary.

Vhile the lead is, on the whole, the most satisfactory for the ,matrixmaking, it is not the desire to be limited to that metal. Any' softmetal or alloy may be used and are yconsidered as. being equivalentscoming within this invention.

From all of the foregoing it is apparent that accurate rubber printingplates can be produced with a minimum amount of equipment and at a verylow cost. Plates pro- Y duced inthe manner described give very accurateregistration of impressions, and the work produced by them, particularlyin color printing, presents a` much better appearance than hasheretofore'been obtained from rubber plates.

While the method and apparatus set forth are highly satisfactory in allrespects, it is obvious that changes in the apparatus and variations inthe separate steps or sequence of steps may be made, all of which comewithin the scope of the claims which follow.

`What is claimed is 1. A method of making metal-backed rubber printingplates which comprises first making a lead-lined mold for the printingface of the plate, supplyin to the mold a quantity of unvulcanized ruber compound, in plastic condition, compressing the com-` pound betweenthe mold and a rigid backing plate treated to cause adhesion of therubber duringr vulcanization, said compression effecting the molding andcausing extrusion of the excess compound, and vulcanizing the rubberwhile it is compressed between the mold and the backing plate.

2. The method of making printing plates which comprises applying a sheetof lead to the engraved or etched face of a master plate and applyingpressure to force the -lead against and in all parts of said face,casting a backing on the lead sheet while in engagement with said facein such away as tol produce a lead-lined mold having its front and backparallel, separating the mold and plate, applying vulcanizable rubberplastic to the lead-lined mold in excess of the amount required to forma printing plate of the desired thickness, applying a previouslyprepared metal backing plate to said plastic, forcing said backing lateand the mold together to mold the rub r and applying vulcanizing heat tovulcanize the rubber and cause it to adhere to the backing plate, andthen removing the mold.

3. The method of making (printin plates which comprises copying 'a esignrom an engraved or etched plate by forcing a lead plate into all parts othe engraved or etched surface of sald plate, pouring on said lead platewhile it is in such contact with the engraved or etched plate a cementin fiuid condition, applying suiicient pressure to the cement While influid condition to force the cement into close contact with all portionsof the lead sheet and then allowing the cement to set, removing theengraved or etched plate from contact with the lead plate, applyingunvulcanized rubber in plastic condltionto the exposed face of the leadplate, and applying molding pressure and vulcanizing heat to saidrubber.

4. A method of making printing plates which comprises embossing in alead sheet, from a master plate, a reversed copy of the matter on theetched or engraved face of the plate, attaching a rigid backing to saidsheet in such a way asto produce a lead-lined mold of a depth which isfrom fifteen to thirty thousandths of an inch less than the totalthickness of the master plate, supplyin said mold with a quantity ofunvulcanize rubber compound in plastic condition in excess of the amountrequired to fill the mold, ap-

plying a backing plate to the supply of compound, said plate havingpreviously been prepared toeffect adhesion of the rubber in the engravedor etched face of a master plate, applying suiiicient pressure to thesheet of lead through a yielding pad of dry aper pulp to force the leadinto and over al portions of said face whereby to emboss in the leadsheet a copy of the matter on said face, casting a backing on said sheetin such a way as to produce a lead-lined mold having the back of themold parallel with the said face of the master plate and the depth ofthe mold less than the thickness of the master plate, removing themaster plate from the lead-lined mold, supplying the interior of saidmold with a quantity of unvulcanized rubber compound, in plasticcondition, in excess of the quantity required to fill the mold, placinga backing plate of electroty e metal on the supply of rubber compound, te face of saiddplate which is in contact with the compoun havingpreviously been Washed with a solution containin copper sulphate, andapplying pressure an heat suiiicient to force the backlngand moldtogether to yproduce a metal-backed rubber printing plate having thesame thickness at all points as the master late.

7. A metliod of making molds for rubber printing plates and the likewhich com rises forming a lead matrix on'the engrave face of a masterplatein such a way as to copy in the matrix the essential rfeaturesrepresented on said face, castin on the back and sides of the matrix arein orcing back while the matrix is still on the master plate, and

applying an air jet around the edges of the' master plate to free theplate from the mold. In testimony whereof I hereto aiiix my signature.

JGHN C. BAKER. A

vulcanizing, and applying pressure and heat suliicient to force thebacking plate and mold together to produce a metal-backed rubberprinting plate having the same thickness at all points as the masterplate.

5. A method of making printing plates which comprises making a lead moldfor producing the design on said plates, supplying said mold Iwith aquantity of unvulcanized rubber compound in'plastic condition, placingon said supply of compound a backing plate composed of lead and antimonyalloy and having the -face in contact with the compound previouslywashed with a solution containing copper sulphate and copper nitrate,and then forcing the backing plate and the mold together to form theprinting plate and extrude the excess rubber, and applying heat tovulcanize the formed plate and attach it to the backing plate.

6. A method of making printing plates which comprises placing a sheet oflead on

